In lens edge grinding machines at present available to the lens grinding industry it is well known to carry a lens, to be ground by rotation thereof relative to the periphery of a rotary grinding wheel, in an assembly which is rockable about an axis under control of a cam which determines the contour shape of the lens and which is axially displaceable along such axis to cater for the curvature of the lens. In such machines it is known to provide another cam for controlling the linear displacement of the assembly and as such further cam is related to the contour cam it is necessary to set up the machine for grinding each particular shape and curvature of lens, and must thereafter be reset even though a similar shape lens is next to be ground when its curvature is different. Furthermore it is known to cause the assembly to move axially to follow the curvature of the lens by means of a part bearing on the face of the lens but this may cause slight scratching or damage to the lens.
This invention relates to control means for machines for grinding the edges of spectable and like lens, in particular for providing a V-rib therearound for the fixing of the lens in its frame or carrier.
The object of the invention is to provide control means for lens edge grinding machines, which may be set up to grind a lens according to size and thickness and required contour shape, and with the control means set for a particular curvature of lens may then be used for grinding further lenses of the same curvature without further adjustment; the control means being utilisable either alone or in conjunction with a lens deflecting element claimed in U.S. Pat. No. 3,562,963 which is for use in the same kind of lens edge grinding machines.
The object of the invention is furthermore to provide such control means comprising a control surface angularly adjustable between a minimum for plane lens to a maximum for lens of some eight to ten diopters and linearly adjustable for size and/or thickness of the lens such that an element, movable with the lens carrying assembly urged to bear on such surface by the bias on such assembly, causes said assembly to follow a presettable curvature pattern during the grinding of the edge of a lens. Thus as said element moves to and fro along said control surface, due to the rocking of said lens carrying assembly determined by the required contour shape of the lens being ground, it axially displaces said assembly to cater for pre-set curvature of the lens related to the contour shape of the lens.
The control surface may be straight or curved and may comprise the edge of a metallic plate rockably mounted in a linearly movable mount. Such plate may be infinitely angularly variable between vertical and some 15.degree. to the vertical or may be so angularly adjustable through a plurality of steps, corresponding to for example lens curvature from 0 to 8 diopters, and be lockable in adjusted angular position. When infinitely variable the locking means may comprise a clamp and when by steps may comprise a, preferably spring-loaded, member engageable in one of a plurality of recesses or apertures.
The control surface plate mount may be linearly movable by a feed screw and is also preferably provided with looking means. It may be provided with a datum mark or indicator movable relative to marks or a scale provided on a non-movable part by reference to which such mount may be set appropriately to particular thickness and/or size of lens.
To ensure such contact of the element with the control surface plate, the lens carrying assembly is biased for movement in appropriate direction by known means such as by spring pressure or the pull of weights, but preferably is effected by magnetic or electro-motive force.
In a known lens edge grinding machine, in which the lens carrying assembly is axially movable along and rockable about a horizontal shaft, there is provided, on such assembly or on a casing enclosing and movable therewith, an armature through which the horizontal shaft extends, and a permanent or electro-magnet is affixed to the end of such shaft, for example on the end bearing thereof, such that the force of such magnet acting on the armature tends to pull the lens carrying assembly axially of the shaft without affecting the rocking movement thereof. In this way the assembly is urged in the direction for the element, conveniently in the form of a projecting stud, to contact with the effective surface of the control surface plate along which it moves due to rocking movement of the lens carrying assembly .